An electronic whiteboard system is a processor-based computing system used to input and output information associated with a software application running on the system. Typically, in accordance with such a system, one or more users “write” on the whiteboard using an electronic writing instrument or optical marker, such as a lightpen. The lightpen permits the user to write with “electronic ink.” Electronic ink is the term given to writing that is electronically captured from and/or electronically projected on the whiteboard without using physical ink. A user's writing, as well as any other desired information, is displayed on the whiteboard which is viewable by the one or more users. The data entered on the whiteboard may then be stored for subsequent use by the application being run on the system. Examples of such whiteboard systems are: Ideaboard by 3M Inc.; e-Beam by Electronics for Imaging, Inc.; SoftBoard by Microfield Graphics, Inc.; SMART Board by Virtual Ink Inc.; and Liveboard, The Office of the Future: Xerox PARC, Wendy Taylor, PC Computing, pp. 192, January 1995.
Whether a single stand-alone system or a collaborative system (a collaborative whiteboard system is a distributed computing system which includes two or more individual electronic whiteboard systems in communication with each other while running a collaborative application), a typical electronic front-projection whiteboard system, as illustrated in FIG. 1A, is comprised of a whiteboard screen 2, an optical marker or lightpen 4, a fixed-position projector 6, a fixed-position camera 8 and a processing system 10. In such a system, the function of projecting images representing a user's writing on the whiteboard screen 2, in accordance with the lightpen 4, is performed by the fixed-position projector 6. As shown in FIG. 1A, the projector 6 has its own imaging optics 7 associated therewith. The fixed-position camera 8, aimed at the whiteboard screen 2 and the lightpen 4, captures an image of the whiteboard and the light emitted by a lamp associated with the lightpen. Like the projector 6, the camera 8 has its own imaging optics 9 associated therewith. Suitable optical and electronic filtering assure that only the lightpen is sensed among possible background clutter and distractions such as other bright objects. As is known, the presence and location of the lamp of the lightpen in the field of view of the camera may be estimated by various signal processing techniques.
The images projected by the projector on the screen, representing the user's writing strokes, are derived from a display screen buffer. The contents of the display screen buffer depend on optical screen marking events such as those generated by the lightpen. The visual effect that the user's strokes are physically being written on the whiteboard, whenever the lightpen is in the pen-down state, is achieved by the projector projecting the trajectory of the optical marker or lightpen path onto the whiteboard.
As is known, the processing system 10 includes processor and memory resources for coordinating the functions performed by the whiteboard screen 2, the optical marker 4, the projector 6 and the camera 8. Accordingly, the system must accurately sense the location of the optical marker on the whiteboard and then project its writing actions onto the whiteboard. One method for accomplishing these tasks is as follows. The camera and its imaging optics are aimed at the whiteboard in order to capture the optical emission from the lightpen. The captured position of the light must then be transformed such that the projected writing trace generated by the projector appears at the tip of the lightpen as it writes. The transformation used to achieve this goal depends on many factors such as the settings and location of the imaging optics of the projector, and the settings and location of the imaging optics of the camera.
A conventional rear-projection whiteboard system is illustrated in FIG. 1B. The system is comprised of a whiteboard screen 2′, an enclosure 3, a lightpen 4′, a reflecting mirror 5, a fixed-position projector 6′, a fixed-position camera 8′ and a processing system 10′. The components and their functions in the rear-projection system in FIG. 1B are essentially the same as those in the front-projection system in FIG. 1A, as described above, with the following exceptions. In the front-projection system, the user is on the same side of the whiteboard screen as the projector, while in the rear-projection system, the user and the projector are on opposite sides of the screen. Also, the screen 2′ in the rear-projection system is typically translucent so that the lightpen 4′ can be tracked by the camera 8′, via the reflecting mirror 5, and so that the user on one side of the screen can view the images projected on the other side of the screen by the projector 6′, via the mirror 5. Like the conventional front-projection system, the projector and camera of the rear-projection system each have their own separate imaging optics 7′ and 9′, respectively.
A problem associated with conventional whiteboard systems is that they require either a sophisticated special-purpose digitizing whiteboard, or a special optical marker that requires electrical power, or both. Since the conventional optical markers contain electronics, these markers tend to be expensive and configured to work with a particular electronic whiteboard system. Attempts have been made to eliminate the need for an optical marker altogether, such as, for example, tracking the tip of a writer's finger. However, this approach suffers due to difficulty in detecting the up/down state of the “writer's finger.”
Thus, it would be highly desirable to provide a simplified, less expensive and easier to use optical marker for whiteboard system applications. In doing so, all complexity and cost is concentrated in a single device which performs the functions of a projector, camera and illuminator.